Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a shank adaptor
for rock-drilling machines provided with at least one side
flushing hole whose axis preferably lies in the same plane
as the axis of the adaptor and which connects the axial
flushing hole of the adaptor with the outside thereof, and
which side flushing hole, together with the axial flushing
hole, serves as a transport passage for flushing medium.
Hydraulically operated machines are now used to an
ever increasing extent in connection with rock drills.
These machines develop large forces, causing the drill to
be sunk to great depths, which requires efficient removal
of the drill sludge, i.e. effective flushing of the drill.
In order to effectively flush away the sludge from the drill
the flushing medium must be maintained at a very high pres-
sure, said medium normally being water or air. In order to
ensure an efficient seal at the loca-tion where the flushing
medium is introduced into the shank adaptor, there is
arranged around said adaptor a flushing head into which the
flushing medium is introduced and from where said medium
passes into the axial flushing hole of the adaptor through
two circular side flushing holes, which may be drilled at
right angles to the axial direction of the adaptor or drilled
at an oblique angle thereto. This type of flushing, with a
special flushing head around the adaptor, is called separate
flushing.
The disadvantage with these side flushing holes,
however, is that they cause fractural impressions, since the
- 2 -
2~
stresses are particularly high in the two regions of that
edge of the side flushing hole which lie in a diametrical
plane through the side flushing hole at right
Z~
angles to the axis of the adaptor. Consequently, frac-ture
of the adaptor is often caused by fatigue cracks extending
from the said two regions of the side flushing-hole edge.
The main cause of such fa-tigue cracks is that, when in
operation, the adaptor is subjec-ted to rotary bending
stresses which are superimposed on the s-tresses originat-
ing from the shock waves.
In order to increase the wear strength and fatigue
strength of the adaptor in its entirety, the adaptor is
normally subjected -to heat treatment, by carburizing the
same. In this way, pressure stresses are obtained in the
surface layer of the adaptor bo-th axially and tangen-tially,
which are intended -to coun-teract the -tensile stresses
occurring in opera-tion~ It has been found, however, that
this carburizing of the adaptor negatively affects the
pattern of tension forces in side flushing holes of circular
cross section. The tangential pressure forces namely add
to the axial tension forces occurring in operation a-t the
edge of the flushing hole whose diameter is at right angles
to the axial direction of the adaptor. It is true that -the
axial pressure forces resulting from the carburizing of the
adaptor initially counteract the negative effects of the
tangential pressure forces, but because of the re-orienta-
tion of the s-tresses in the carburized surface zone as a
result of the shock stresses occurring in opera-tion, i-t
has been found tha-t the axial pressure s-tresses are rapidly
reduced, and hence the aforementioned positive effect
becomes negligible.
When -the side flushing hole of circular cross sec-tion
are drilled at an oblique angle to the adaptor, a certain
-- 3
reduction in the stresses is obtained in the two afore-
mentioned regions at the edge of the flushing hole lying
in the diametrical plane through the flushing hole àt
right angles to the axis of the adaptor, owing to the
fact that the contours of the edge of said side flushing
hole obtain an elliptical shape. Since, however, the side
flushing hole has a circular cross section, more than one
hole is required, normally two, since the circular side
flushing hole can not be given an excessively large diameter,
although the cross sectional area of the flushing holes must
still correspond substantially to the area of the axiaL
flushing hole on the adaptor.
An object of the invention is to provide a
shank adaptor provided with a single side flushing hole hav-
ing a cross sectional shape such that stress concentration
at the outer edge of the side flushing hole is reduced while
decreasing hole-edges sensitive to fractural impressions
by half, which also results in a reduction in the proba-
bility of fatigue cracks caused thereat by the rotary bending
forces on the adaptor.
In accordance with the present invention,
there is thus provided a shank adaptor for a rock-drilling
machine, provided with at least one side flushing hole which
connects an axial flushing hole of the adaptor with the out-
side thereof and which, together with the axial flushing
hole, forms a transport passage for flushing medium. The
., .., . ~
2~4
shank adaptor of the invention is characterized in that the
side flushing hole has an oblong cross-sectional shape with
tho longitudinal axis of the oblong parallel to the
longitudinal axis of the shank.
Preferably, the side flushing hole extends
along an axis which lies in the same plane as the axis of the
adaptor.
The ratio of length to width of the cross-
section of the side flushing hole is preferably at least
3:1.
Because the cross-sectional area of the flush-
ing hole in the adaptor according to the invention can be
made greater, due to the fact that the hole has an oblong
cross-sectional shape parallel with the axial direction of the
adaptor, more than one single side flushing hole is no longer
required, since the cross-sectional area of the hole can be
made equal to the cross-sectional area of the
- 4a -
.~
~6~Z14
axial flushing hole of the adaptor. Because the side flush-
ing hole n~w lies on only one side of the adaptor, the risk
that the hole is located in the zone of the largest stresses,
with respect to the rotary bending forces in operation,
is greatly decreased.
The invention will now be described in more detail
with reference to the accompanying drawings, in which Fig. 1
is a side view of one embodiment of a shank adaptor according
to the invention, and Fig. 2 shows in section the flushing
hole in the adaptor of Fig. 1.
The illustrated adaptor has a hammer,surface 1 for
the hammer piston of the drill machine, splines 2 for rotating
the adaptor during a drilling operation, and an external
screw thread 3 on which a jointing sleeve can be screwed~
Fig. 2 is a sectional view through a flushing head 4. The
flushing head is not shown in Fig. 1. The flushing head
encloses the side flushing hole 5 of the adaptor, said hole
5 opening out into the axial flushing hole 6. I'he head 4 is
provided with an inlet connecting means 7 on which, for
example, a flushing-water hose can be connected. ~he head 4
is slidably mounted on the adaptor via sealing rings 8. The
side flushing hole 5 extends at right angles to the axial
flushing hole 6, the hole being made by means, for example,
of a shank end miller, whereby the two ends 9 obtain the form
of half cylinders while the sides 10 extend parallel to the
direction of the adaptor axis, the length of the hole between
the two ends 9 being approximately three times the width of
-- 5 --
, .
the hole.
Although the shank adaptor according to the
invention has been described with reference to a particular
embodiment thereof, it is not restric ed thereto but can be
modified
- 5a -
-
14
wi-thin the scope o:F the claims.
